The present invention relates to telecommunications signal transmission equipment. More particularly, the present invention relates to conversion of signals from balanced twisted pair cables for transmission via unbalanced coaxial cable, and from unbalanced coaxial cables for transmission via balanced twisted pair cables.
In the professional audio and video industry, digital audio signals are typically transmitted via balanced twisted pair cables. These twisted pair cables typically operate at a signal impedance of 110 ohms. However, transmitting digital audio signals over longer distances using the balanced twisted pair cable is somewhat problematic. The signal degrades as it passes through the twisted pair cable conductors. Amplification devices to magnify and retransmit the digital audio signals are often required if the digital audio signal transmission length is greater than 150 feet over twisted pair cables.
To address this issue, users are known to pass digital audio signals through a digital audio impedance transformer and transmit the transformed signal via unbalanced coaxial cable at a signal impedance of 75 ohms. Using the unbalanced 75 ohm coaxial cable, the maximum cable distance for transmission without amplification devices can be extended.
The nature of the signal conversion process is such that a single digital audio impedance transformer can handle both unbalanced and balanced signals and the higher and lower impedance conversions. Thus a single transformer can be used to handle bi-directional signal flow.
One known device which handles this signal conversion process is an in-line digital audio transformer for transforming signals between a single twisted pair cable and a single coaxial cable. This in-line device is mounted in the digital audio signal transmission path between cable ends and is then left on the floor or ground subject to environmental exposure and other physical abuse. Often, if multiple circuits with these devices are in one area, organization and identification of the devices can be quite difficult.
Sometimes in these digital audio circuits, voltage attenuation is required, due to an incoming signal with a voltage amplitude beyond the capabilities of a downstream device to handle. This voltage attenuation function can be incorporated into the digital audio transformer device in the form of an attenuation pad. An attenuation pad works by controlling the dB loss in the transformer circuit, thereby moderating the voltage to a more suitable range. The known single circuit in-line devices include attenuation pads of fixed voltage attenuation value within the device. Unfortunately, a fixed attenuation value does not permit alterations of the overall signal transmission environment, if changes are needed. If these transmission environment conditions do change enough to require the alteration of the attenuation value within the in-line digital audio impedance transformer, the entire transformer will need to be switched out to ensure the resulting output voltage is at a proper amplitude for the downstream device.
The known in-line transformer devices typically have a coaxial connector on the coaxial cable side and an XLR connector on the twisted pair side. XLR connectors are relatively expensive compared to alternative connectors, but XLR connectors have traditionally been used in transmitting audio signals. The known in-line devices are also typically cylindrical or barrel-shaped and have machined housings. Manufacture and assembly of such devices is labor intensive and therefore more costly.
Further improvements are desired for signal transformers, such as for digital audio signal transmission systems to address the above concerns or other concerns.
In one aspect of the present invention, a transformer module includes one or more impedance transformer circuits in a chassis-mountable housing with connectors mounted on the front and rear of the module for attaching twisted pair wires and coaxial wires, and circuitry including baluns connecting pairs of front and rear connectors. The circuitry may include removable attenuation pads adjacent to one of the connectors of the circuit to which the attenuation pad is attached. The circuitry may include provisions for the baluns to be removably inserted, so that baluns of different impedance levels may be utilized. The module may also have a cable clip adjacent to the connectors to aid in cable management.
A further aspect of the present invention includes providing a digital audio impedance system made up of a plurality of the digital impedance transformer modules of the present invention mounted in a chassis.
Another aspect of the present invention is to provide a multi-circuit impedance transformer module for use with a chassis with linearly arrayed connectors mounted on opposite faces of the module with transformer circuits including baluns. Attenuation pads can be mounted adjacent to one of the sets of connectors.
A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.